1. Field of the Invention
The present invention is related to optical communication systems and, in particular, to positioning optical fibers within optical communication systems.
2. Background of the Invention
The primary function of an optical communication system is to transmit an optical signal from an optical transmitter to an optical receiver with minimal distortion of the optical signal. The optical transmitter converts an electrical signal into optical form and launches the resulting optical signal into an optical fiber. The optical fiber emits the optical signal into free space. An optical detector detects the optical signal in free space and couples the optical signal to the optical receiver.
For optimal communication of the optical signal from transmitter to receiver, optical fibers (or optical signals) on the transmit end must be aligned with detectors on the receive end. Because optical terminals that house transmitters and receivers are typically located in architectural structures (buildings, poles, etc.), which sway under the effect of wind, rain, sleet, snow, etc., or vibrate under the effect of human, mechanical, or natural phenomena, the optical fibers may become misaligned. Slight movement of the optical fiber, on the order of microradians (e.g., a microradian is an angular rotation of one part in 6.28 millions of a full circle) may be sufficient to cause misalignment. To minimize the chances of interrupted communications, the optical fiber must be rapidly and accurately realigned.
There are devices available today for positioning optical fibers, but they have limitations. For example, one type of device uses staged position controllers. These devices are expensive, slow, and only provide horizontal and vertical control.
Another type of device is a dither controller with lock-in amplifiers. These devices tend to be cascaded and time-shared using time division multiple access (TDMA) approaches. Time-shared/cascaded techniques tend to be cumbersome and tedious when attempting to implement horizontal and vertical control, and horizontal and vertical control cannot be performed simultaneously.
The present invention is directed to an optical fiber positioner to position an optical fiber in several degrees of freedom. The optical fiber positioner includes a digital controller to code digital degree of freedom value signals using a unique orthogonal code for each degree of freedom, a digital-to-analog converter bank coupled to the digital controller to convert coded digital degree of freedom value signals to coded analog degree of freedom value signals, an actuator coupled to the digital-to-analog converter bank to move an optical fiber based on the coded analog degree of freedom value signals. In operation, an optical fiber emits an optical signal having the coded analog degree of freedom value signals into free space. The optical fiber positioner includes an optical detector to detect the optical signal from free space and to recover coded analog error signals based on the coded analog degree of freedom value signals, and an analog-to-digital converter coupled to the optical detector to convert the modulated analog error signals to modulated digital error signals. The digital controller is coupled to the analog-to-digital converter to detect coded digital error signals using the unique orthogonal code.